1. Field of the Invention
The present invention relates to an actuator for an optical pickup apparatus used in the reproduction and/or recording of a compact disk (CD), a digital video disk (DVD), and the like.
2. Description of the Related Art
Conventionally, an optical pickup apparatus having an actuator of an axially slidable type is known in which a lens holder holding an objective lens is provided in such a manner as to be slidable with respect to a supporting shaft in its axial direction and to be rotatable about the axis. An electrically driving circuit is formed by a pair of tracking coils and a focusing coil which are fitted to the lens holder as well as a pair of yokes and a pair of magnets formed of a magnetic material and respectively disposed on both sides of the lens holder. The arrangement provided is such that as drive currents are allowed to flow across the tracking coils and the focusing coil, by means of the lens holder the objective lens is rotated in a tracking direction about the axis of the supporting shaft and is moved in a focusing direction along the axis of the supporting shaft.
However, with the conventional actuator of the axially slidable-type optical pickup apparatus, since the arrangement provided is such that a yoke member in which a pair of yokes are provided on a baseplate portion is fixed by a plurality of screws to an actuator base member which is attached to a main base member, the fixing strength of the yokes provided for the purpose of obtaining a sufficient driving force by strengthening the magnetic forces of the magnets is insufficient. Therefore, trouble occurred in that the yokes resonate in a high-frequency range at a resonance frequency of 5 to 8 kHz in correspondence of the oscillation of the lens holder. In the case where the yokes resonate in a high-frequency range at the aforementioned resonance frequency, there arises a problem in that servo control characteristics of the actuator of the optical pickup apparatus at the time of effecting focusing and tracking deteriorate, and the response characteristics of the lens holder become poor, thereby making it impossible to effect high-accuracy servo control.
Apart from the above-described case, the following two techniques are known as countermeasures against the unwanted resonance in the optical pickup apparatus. One is an optical-head mounting mechanism (refer to Japanese utility model publication No. 5-4313) in which in a case where oscillation has occurred in the optical head as drive systems for tracking and focusing are driven at a tip of the optical head, the resonance of an optical head-mounting base due to its effect is suppressed. The other is an objective-lens driving apparatus (referred to JP-B-7-70081) in which the jumping out of a drive coil to the magnet side is prevented, and improvements are made in the high-frequency resonance characteristics of the drive coil.
With the above-described optical-head mounting mechanism, however, a tracking control magnet yoke, which is provided so as to allow a tracking control air-core coil of the optical head is swingably inserted therethrough, is provided with an L-shaped weight by means of a resilient member, whereby the mass of the optical head-mounting base is increased to make it difficult for the resonance due to the effect of the resonance of the optical head to occur, or the resonance point is changed to a location which does not affect focusing or tracking, and the oscillation is absorbed by the resilient member, so as to alleviate the adverse effect on the optical pickup. Accordingly, since such an arrangement basically differs in construction from that of the actuator in the above-described axially slidable-type optical pickup apparatus, this arrangement cannot be used as a means for eliminating the unwanted resonance caused by the yoke of the actuator in the above-described pickup apparatus.
On the other hand, with the above-described objective-lens driving apparatus, a free side of the drive coil is pressed down by the tension of a wire to prevent the jumping out of the drive coil toward the magnet side, and the free side of the drive coil is fixed by an adhesive-reinforcing layer to enhance the rigidity of the drive coil, thereby raising the resonance point of the drive coil to a higher range to improve the high-frequency resonance characteristics. Accordingly, even if a change is made in some portion of it, such a construction cannot still be used as a means for eliminating the unwanted resonance caused by the yoke of the actuator in the above-described axially slidable-type pickup apparatus.